Bitumen (or asphalt) is the heaviest portion from the oil distillation process. Due to the different origins and distillations processes of such oils, the resulting bitumen may have a wide range of properties and characteristics. In the present invention, bitumen refers not only to the product from oil by direct distillation or from distillation of oil at reduced pressures, but as well to the products coming from the extraction of tar and bituminous sands, the products of oxidation and/or fluxation with carbonated solvents including paraffins and waxes, as well as solvents derived from vegetable oils, of such bituminous materials, and also blown or semi-blown bitumens, synthetic bitumens using renewable materials (such as those described for example in FR-A-2 853 647 and in FR-A-2 915 204), tars, oil resins or indene-coumarone resins mixed with aromatic and/or paraffinic hydrocarbons and the mixtures of such, the mixtures of such bituminous materials with acids and the like.
The main application for bitumen is in asphalt mixes where the bitumen is mixed with mineral aggregates that can be of different sizes, shapes and chemical natures, said bitumen performing the function of binder for the said aggregates. These asphalt mixes are particularly used for construction, repair and maintenance of sidewalks, roads, highways, parking lots or airport runaways and service roads and of any other rolling surfaces.
Mineral aggregates used in asphalt mixes generally are products from quarries, and are more and more often used in admixture with aggregates recuperated from previously fabricated asphalt mixes. Such recuperated aggregates are known under the generic name of RAP, i.e. Reclaimed Asphalt Pavement (see for example AFNOR XP P98-135, December 2001, or Asphalt Handbook, MS-4, 7th edition, published by the Asphalt Institute, USA).
RAPs also include recycled asphalt mixes wherein the mineral aggregates are replaced in whole or in part with other common components, such as, by way of limiting examples, organic and inorganic fibers (e.g. glass, metal or carbon fibers, cellulose, cotton, and the like), polymers (e.g. polypropylenes, polyesters, poly(vinyl alcohol)s, polyamides, polyurethanes, poly-ureas, EVA and SBS polymers, and the like).
Of particular interest are the recuperated or recycled aggregates, commonly known as RAP. These aggregates are the result of milling (or other grinding method) of previously constructed pavements, which are generally damaged and need to be replaced. These recycled aggregates contain bitumen (the one used as binder during their previous fabrication).
Other sources of bituminous products that may also be recycled into pavement fabrication are for example roofing products (such as shingles or waterproofing membranes, as well as waste materials coming from their production), isolation or sound damping materials, and the like.
In the description of the present invention, “recycled bituminous product” is understood as any kind of manufactured product comprising bitumen as one of its components, where the said manufactured product comprising bitumen has been previously used or discarded after production. Non limiting examples of such recycled bituminous products are the reclaimed asphalt pavement (also known as RAP) obtained from the milling of roads and other rolling surfaces, waterproof membranes, bituminous shingles used in roofing (reclaimed asphalt shingle, RAS), sound-proof panels, wastes coming from their production the mixtures of two or more thereof, and the like.
There are nowadays indeed economically and environmentally interests in incorporating recycled bituminous products (aggregates and/or other bitumen-bound components as described above) into new asphalt mixes. Significant savings may be obtained by re-using the bitumen already present in such recycled bituminous products, since the binder is usually the most expensive component in asphalt mixes. Moreover, bitumen is non renewable. Additionally, the extraction and production of bitumen from its original sources (crude oil) have an important impact of the environment, and such impact is lowered when using RAP.
Nonetheless, constraints on quarries make it difficult to extend existing quarries or create new quarries for larger exploitation. As a result, aggregates are also considered as non renewable materials.
The addition of recycled bituminous products, including the binder contained in them, is however not an easy process. The bitumen contained in such recycled bituminous products is usually aged, and thus harder than fresh regular pavement bitumen. This is one of the reasons why a limited amount of bituminous recycled products, such as RAP, is generally added into asphalt mixes.
There are several methods to add RAP or other recycled bituminous products into an asphalt mix. For example, before its incorporation into the mix, RAP may be preheated (generally above 100° C.), without exceeding a certain limit in order to avoid smokes and further oxidation of the bitumen. An advantageous aspect of this method is that the binder for RAP is softened, and thus its incorporation and mixing together with the fresh bituminous binder is facilitated. This process however requires the investment to dedicated equipment to preheat the RAP.
Another approach consists in introducing the recycled product at ambient temperature directly into the hot mixer (generally at a temperature of above 100° C.), said mixer containing virgin aggregates. The heating of the recycled product takes place and then the mixing with hot fresh (or virgin) bitumen is realized. Although this approach presents the advantages of requiring little equipment investment, it is more difficult for the aged binder contained in the RAP to be mixed with the virgin bitumen due to the limited contact time before cooling. Additionally, smoking can be significant when contacting RAP and the heated virgin aggregates.
All these methods using RAP lead to the conclusion that although the amount of fresh aggregates may be lowered, fresh bitumen still needs to be added in large amounts since the aged bitumen present in the RAP is not at all or not completely reusable.
Facing this problem, the skilled artisan already tried to find solutions aiming at softening the bitumen present in the recycled bituminous products, so that the RAP aged bitumen is reusable to a larger extent, the amount of fresh bitumen is lowered, and the mixing with the rest of the other components is easier.
A solution that is presently commonly used consists in compensating the hardness of the aged bitumen contained in reclaimed bituminous products by adding oils (aliphatic, aromatic or combination of both) and/or other solvent-like products. These oils and other solvent-like products soften the aged bitumen present in the reclaimed bituminous products, making it easier to release it and mix it with the other components of the asphalt mix. These oils and/or solvent-like products are sometimes referred to as “rejuvenators” or “rejuvenating oils” or “rejuvenation oils”.
When used in the description of the present invention, the expressions “rejuvenator”, “rejuvenating additive”, “rejuvenating agent” mean any additive that eases (or facilitates) the mixing and incorporation of a recycled bituminous product into fresh bitumen or into an asphalt mix, during an asphalt mix production process.
For example, U.S. Pat. No. 6,214,103 discloses the use of a non-volatile oil, chosen from petroleum hydrocarbons, natural oils or synthetic hydrocarbons, in amount between 0.15% and 0.5% by weight with respect to the total amount of asphalt mix. This allows the incorporation of between 30% and 80% of RAP in the preparation of asphalt mixes.
U.S. Pat. No. 6,186,700 discloses the use of a rejuvenating oil, emulsifier, recycled asphalt, pavement asphalt concrete oil, anti-strip additives and liquid silicone for the preparation of a pavement and patch material for paving surfaces. The emulsifier additive disclosed in this patent assists in mixing the composition when there is water or a moisture content either in the recycled asphalt roofing waste or aggregate.
In U.S. Pat. No. 7,811,372, the use of palm oil is described as a rejuvenating agent composition containing also bitumen. In the examples, amounts of palm oil in the order of 5% in weight with respect to the total bitumen content were used to obtained physical properties of the bitumen close to fresh bitumen.
GB 2 462 371 describes the use of plant-derived oils in amounts between 2% and 20% of the total mass of bitumen as a rejuvenator of asphalt.
In US 2006/0215483, the use of a terpenoid liquid, such as modified soybean oil, canola oil or corn oil, is used in combination with bitumen for preparing asphalt mixes containing RAP. The content of such terpenoid liquid claimed to be necessary is between 4 wt % and 40 wt % with respect to the amount of fresh added bitumen.
In all the above examples, a relative large quantity of such rejuvenators is necessary to improve the incorporation of RAP into an asphalt mix. One drawback is the necessity of large rejuvenator storage facilities. Moreover, although these rejuvenators may facilitate the incorporation of RAP or other recycled bituminous products, such rejuvenators are generally not efficient enough: in a number of cases, only a partial dissolution of the aged and hard reclaimed binder occurs, leading to only a partial mixing with the rest of the asphalt mix. This results in an asphalt mix with poor mechanical properties due to the heterogeneity of the asphalt mix components.
Also, the relatively high amount of rejuvenator oils may lead to asphalt mixes with relatively poor mechanical properties. Still another problem that may be encountered is the evolution over time of the mixtures containing such additives. Shortly after preparation, the rejuvenator may have not completely dissolved the hard (aged) bitumen, the prepared asphalt mix may be too soft (mainly because of the soft added virgin bitumen), so that early rutting often occurs. The larger the quantity of RAP introduced, the larger the amount of rejuvenating oil to be used to soften the aged bitumen, and the higher the risk of rutting.
Later after preparation, say after the rejuvenator may have completely dissolved the hard bitumen or may have been evaporated, a very hard asphalt mix is observed, so hard that it may become brittle and not appropriate for a number of applications, such as rolling pavements.
Therefore, it is of practical interest to find out alternative to the commonly used rejuvenators in order to still improve the incorporation of aged hard bitumen present in recycled bituminous products.
WO 2010/017283 discloses a cold-in-place recycling method comprising mixing an ethoxylated diamine surfactant, water and an asphalt binder, the resulting foamed composition being mixed with 100% milled recycled pavement aggregates. This application teaches that the binder is coated or more uniformly spread over the particles. This is a clear teaching that the reclaimed binder plays no role in the invention of this application, i.e. the reclaimed binder is not rejuvenated.
Warm asphalt mixes containing up to 30 wt % of RAP are presented in WO 2009/033060 where they are prepared from functionally dry asphalt binder and a lubricating additive. Functionally dry asphalt binder refers to asphalt binder composition that contains less water or moisture than is routinely used in conventional or known warm mixes. The technique disclosed in this international application is therefore not applicable to asphalt binders that are conventionally and routinely used for paving rolling surfaces. Again, this application does not teach any rejuvenating effect of the reclaimed binder.
A first objective of the present invention is the provision of alternative additives allowing improving the mixing of recycled bituminous products in the preparation of asphalt mixes. Another objective consists in providing additives that allows for the use of recycled bituminous products in larger amount during the preparation of asphalt mixes.
Still another objective is the provision of new additives leading to the lowering of the amount of fresh bitumen in the preparation of asphalt mixes with recycled bituminous products. According to a further objective, the present invention proposes to use alternative additives that further enhance the mechanical strength of asphalt mixes prepared with recycled bituminous products.
All the afore-mentioned objectives, as well as even others that will appear in the below description of the present invention, are met in all or in part when using alternative additives to the well known rejuvenators in the preparation of asphalt mixes with recycled bituminous products.